The present invention relates generally to fountain pens and more specifically to the refillable ink cartridges used in fountain pens.
In general there are three methods of supplying ink to a fountain pen: (1) dipping the nib directly into an ink well to coat the same with ink; (2) providing a disposable ink cartridge that is inserted into the body of the pen such that fluid communication is established between the ink cartridge and the nib to supply the same with ink; and (3) providing a refillable ink cartridge that is either removable from or integral with the body of the pen and such that fluid communication is established between the ink cartridge and the nib. The refillable ink cartridges are often referred to as piston converters by the skilled artisan. A piston converter, in general, is a hollow body with a plunger slidably disposed therein. The hollow body is fluidly connected at one end to the nib of a fountain pen. In order to fill a piston converter with ink, the plunger is pushed forward into the hollow body, the nib of the pen is substantially submerged into a well of ink (in the case of a removable type converter, an end of the hollow body is inserted into the well of ink), and the plunger is withdrawn, thereby drawing ink into the hollow body; the operation is analogous to drawing fluid into a syringe. The plunger remains in the hollow body, thereby sealing one end of the hollow body. The second end of the hollow body, as mentioned above, is in fluid communication with the nib. After filling the piston converter the pen can be used until the ink runs dry, after which the process is repeated to fill the piston converter with ink again. In some cases a removable piston converter can be replaced by a disposable cartridge if the user prefers disposable cartridges over piston converters.
In one prior art piston converter the plunger is moved within the hollow body by a drive mechanism. The general concept of the drive mechanism uses a plunger shaft connected to the plunger and a drive member fixed relative to the hollow body and engaged with the plunger shaft. The plunger shaft has either external or internal threads, and the drive member has threads that mate with the threads of the plunger shaft. Because the drive member is fixed relative to the hollow body, turning the drive member causes its threads to rotate, which causes the plunger shaft to move longitudinally relative to the hollow body. Thus, turning the drive member moves the plunger within the hollow body permitting a user to draw ink into the hollow body.
One disadvantage to using this drive mechanism for piston converters is that the drive member is often inadvertently rotated, thereby causing a relatively large quantity of ink to discharge out of the nib. This inadvertent ink discharge can stain clothes, hands, fingers, it can ruin documents and virtually anything else it contacts. Likewise, inadvertently rotating the drive knob may cause air to be drawn into the hollow body, thereby affecting the performance of the pen. Thus, there is a need in the art for a piston converter with a drive mechanism that a user selectively activates, which, among other things, will substantially prevent the accidental discharge of ink from a fountain pen.
A preferred embodiment of a piston converter in accordance with the present invention includes a hollow body having a distal end and a proximal end, a plunger assembly, a metering knob, a drive rod, and an engagement rod. The distal end of the hollow body provides fluid communication between the hollow body and a nib of a fountain pen. The plunger assembly, preferably a plunger attached to a plunger rod, is slidably disposed in the hollow body. The metering knob is configured to engage the plunger assembly, preferably the plunger rod, to advance or withdraw said plunger within said hollow body. The drive rod is configured to engage the metering knob such that turning the drive rod will turn the metering knob, which will advance or withdraw the plunger assembly. An engagement end of the engagement rod is configured to selectively engage the drive rod, preferably by drawing or pushing the engagement end into or out of a cavity within the drive rod configured to engage the engagement end, such that when in the engaged position turning the engagement rod will cause the drive rod to turn which will cause said metering knob to advance or withdraw said plunger within said hollow body.